DC servo speed control of an inkjet print head transport system using a phase-locked loop

A low-cost servo control system has been developed to regulate the speed of a belt driven moving carriage. It is used by a print head transport system which is designed for an inkjet printer developed by OES/ITRI in Taiwan. The servo controller is realized by a phase-locked loop with a DC servo motor. The phase-locked loop includes a lead-lag compensator which is designed based on the experimental system identification of the print head transport system. The experimental transfer function of the system is obtained under a set of sweeping sinusoidal excitation. On the basis of that model, a lead-lag compensator is then designed by using the root locus method. The compensator is proven to be effective in regulating the speed variation of the carriage within 10% while the carriage moves at 33 inches/sec. Experiments are performed to verify the effectiveness of the lead-lag compensator. This approach has made it possible for inkjet printers to be realized to demonstrate extreme improvement in printing throughput using low-cost ICs.